Planning a

Introduction:

Catalysts are chemicals which make it easier for chemical reactions to occur. This occurs because the catalyst lowers the activation energy, or amount of energy needed to get the reaction to occur spontaneously. Enzymes are one type of catalyst. They are proteins and help the reactions of living cells to occur at temperatures the cell can survive at. Enzymes are 3-dimensional proteins which have a shape area on their surface known as the active site. It is here that the substrate, or reactant/s of the reaction must fit, usually like a lock and key. Because of this lock and key fit of substrate to enzyme, one enzyme usually catalyzes only one reaction. The enzyme usually speeds up the reaction by either getting the substrate/s together and or oriented in such a way that they can react more easily, or by helping to flex and break chemical bonds.

Catalase is an enzyme found in cells that catalyzes the natural breakdown of hydrogen peroxide. Peroxides are often formed by breakdown of poisons or preservatives found in our diet. If the peroxides increase in number within the cell, the cell may die. Catalase helps remove this deadly chemical by converting it to the harmless products water and oxygen. The balanced equation for this reaction is 2H2O2 ----catalase-----> 2H2O + O2. The oxygen that is produced is a gas, which bubbles out of the liquid. If the reaction mix contains a drop of soap, the oxygen bubbles become coated with soap, producing a thick foam that persists for a minute or so. This allows measurement of the foam, indication how much oxygen that is being produced.

A number of factors affect how quickly enzymes work upon their substrates. Some of these factors include temperature, pressure, substrate concentration, enzyme concentration, and presence of inhibitory molecules. The variable being studied here is "how temperature affects reaction rate".

Sources:

Wikipedia: http://www.wikipedia.com/enzyme.htm

Wikipedia: http:www.wikipedia.com/catalase.htm

Textbook: "Biology" by Crow and Benson, pp. 76-78 UCLA Press, 1876.

Question :

What is the effect of the catalase concentration upon the reaction rate of a reaction involving the decomposition of peroxide using the enzyme catalase?

Hypothesis:

As the concentration of catalase increases, the reaction rate of the decomposition of peroxide via catalase will increase and then level off. This occurs because as more substrate is used, more enzymes become involved in the reaction, increasing the reaction rate. The reaction does not occur at its maximum rate yet because some enzymes are sitting around unused because there is not enough substrate to fit them.

When the substrate concentration is raised high enough, the reaction rate will level out and become constant because at that time, all of the enzymes are being utilized. At that point, there is more substrate than enzyme and some of the substrate must wait for enzymes to become available, stretching the reaction out for a longer period, but again at a constant rate.

An analogy for this hypothesis might be a factory that makes a certain make of sports car. Assume that the assembly lines are like the enzymes and the auto parts are the substrate. If there are 10 assembly lines, but only enough parts are available to involve 3 of the assembly lines, then 3 cars might be made per unit time. If more parts are available, say enough for all 10 assembly lines, then the factory can work at its maximum rate and make 10 cars per unit time. If there are parts for 15 assembly lines, only 10 cars can still be made per unit time because there aren't enough lines for all the parts.

Independent Variable: % substrate concentration

Dependent Variable: reaction rate (data collected as height of oxygen foam produced and time of foam production)

Positive Control: A test tube with 100% peroxide, drop of soap, and the catalase added.

Negative Control: A test tube with 0% peroxide, drop of soap, and the catalase added (so there is no reaction) and

A test tube with 100% peroxide, drop of soap, but no catalase added (so there is no reaction)

Important Variables to Keep Constant:

a) Temperature

b) Air pressure

c) Catalase concentration

d) Age of catalase and peroxide (both decompose with age with resulting reduction in concentration)

e) Obtain all catalase and peroxide used from the same source to maintain consistency.

f) Ratio of peroxide to enzyme present during the reaction (may affect whether the reaction increases or levels off).

g) Volumes of peroxide and enzyme used. (Larger quantities used means less chance that a wayward drop or small change influences the results, and provides a greater chance for a wider difference in results (important when comparing standard deviation)).

h) Diameter and height of test tubes.

i) Number of drops of soap added

j) Measurement of foam (specified as part of procedure)

k) Timing of foam production (specified as part of procedure)

l) Labeling of beakers and droppers of catalase, peroxide, soap and water.

m) Cleanliness and dryness of beakers, graduate cylinders and droppers.

n) How the drops of materials are added (affects the volume of the drop)

o) Application of materials to the bottom of the test tube, rather than the side.